Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must carry the behavioral load. It usefully discloses the authorization gate (agent-writes switch), that the operation is non-merging, and that the target repo is the run binding — genuine value beyond the schema. It says nothing about failure modes, e.g. what happens if the head branch was never pushed or a PR already exists for that head/base pair.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, no filler, with the action stated first and the authorization constraint immediately after. Nothing repeats the schema or the name.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists so return values need no explanation, and all parameters are covered in the schema. The description supplies the two things structured fields cannot: the write-authorization gate and the implicit repository binding. Sufficient for an agent to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all six parameters are already documented in the schema; baseline is 3. The description adds only one piece of meaning beyond that — that omitting `github` resolves to the run's bound repo — and says nothing about head/base relationships.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('Open a pull request') scoped to 'this run's repository', and immediately clarifies it does not merge, which separates it from the github_merge sibling. An agent can tell what it does without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Names a concrete prerequisite ('Requires the org's agent-writes switch') and the non-merging scope, and explains the default repository binding ('The repository is the run's bound github='). It stops short of explicitly routing to github_merge for merging or to github_pr_get/github_pr_checks for follow-up, so alternatives are only implied.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.